1. Field of Invention
This invention relates to methods for manufacturing copper-bismuth alloys, and to metal compositions used in said manufacturing.
2. Description of Related Art
Leaded brass and bronze ingot alloys are produced by blending several grades of feedstock metal in an electric or rotary furnace. The grades of feedstock used to produce these alloys often contain metallic impurities, such as aluminum, silicon and iron, along with non-metallics, such as plastic and dirt. These impurities are removed from the melt through refining of the molten bath or by the introduction of chemical fluxes to the molten bath.
Over the past ten years, there has been a steady increase in the demand for lead-free brass and bronze alloys, as replacements for leaded brass and leaded bronze alloys. This is largely due to the increasing worldwide demand for lead-free plumbing products.
Copper-bismuth alloys have been proposed as alternatives to leaded alloys. For example, U.S. Pat. No. 5,330,712 discloses that suitable brass alloys can be prepared by substituting bismuth for lead in the alloy composition. The resulting lead-free copper-bismuth alloys can be substituted for conventional leaded brasses in plumbing fixtures and other applications. See also U.S. Pat. No. 5,487,867.
Most preferred among the copper-bismuth alloys are C89833 and C89836 alloys. These alloys are considerably more expensive than the leaded alloys that they replace, based in part on the need to use high grades of copper in the manufacturing process so as to avoid lead contamination within the resulting alloys.
Lead-free casting alloys, such as C89833 and C89836, are considered to be a higher grade alloys compared to leaded brass and leaded bronze alloys. This is because, in order to ensure that the lead content within these alloys is as close to zero as possible, each melt is primarily composed of pure elements such as pure copper, tin, zinc and bismuth. Each of these alloys is also considered to be a much higher grade alloy because of the higher production costs.
Alternatively, higher grade alloys can be produced primarily with blends of various grades of feedstock metals, which generally have variations in metal chemistries within the same grades of feedstock, resulting in melts which might require adjustments to the chemistry by means of refining, dilutions or additions of certain elements prior to the casting of the ingot.
Both leaded and lead-free ingot alloys are typically supplied to foundries as a cast ingot with a certified analysis. This ingot is then re-melted and cast into a specific product.
Traditionally, high production foundries require a cast ingot in order to continually keep their furnaces full, and to keep up with high volume pouring rates. Feeding a furnace to capacity with the pure elements copper, tin, bismuth and zinc in the precise amounts necessary to produce C89833 and C89836 is a challenge requiring expertise and equipment that are not found in the average foundry.
It is therefore desired to address one or more of the foregoing issues by providing an improved method for producing substantially lead-free copper-bismuth alloys. It is further desired to provide such a method, wherein the copper-bismuth alloys are produced from scrap metal. It is still further desired to provide a simplified method for producing substantially lead-free copper-bismuth alloys, which can be reliably practiced in an average foundry.